Method of recovering valuable metals from the vrds spent catalyst

ABSTRACT

The present invention discloses method of recovering valuable metals, such as vanadium, molybdenum, nickel from the catalysts spent in the VRDS process for desulfurization of pertroleum. The method comprises leaching water-insoluble reactants after reacting the pre-treated waste crystals in solution of sodium hydroxide, maintaining the filtrate at pH 9.5 by adding sulfhuric acid or hydrochloric acid and then heating the filtrate, removing aluminium oxide from the soltuion, aerating the filtrate continously or priodically and agitating the filtrate below pH 1 at 80-100° C., thereby precipitating molybdenum oxide and vanadium oxide, and leaching and washing the precipitated molybdenum oxide and vanadium oxide.

TECHNICAL FIELD

This invention relates to a method of recovering metals, such asvanadium, molybdenum, nickel (hereafter, referred to as “valuablematals”), from the catalysts spent in the ‘Vacuum ResidueDesulfurization’ (VRDS) process for desulfurization of pertroleum.

BACKGROUND ART

There is known a conventional method for recovering the valuable metalsfrom the spent catalysts in the VRDS.

The conventonal method comprises removing the soaked oil from the spentcatalysts by heating the catalysts over the boiling point of oil andthus evaporating the soaked oil from the catalysts. The spent catalystsare roeated at 400˜600° C. in the furnace with air (oxyzen) supplied tooxidize sulfur and metals in the catalysts. In the roasting process, thesulfur is oxidized into SO_(2,) and further the metals, such asmolybdenum, vanadium, nickel and cobalt are oxidized into MoO₃, V₂O₅,NiO, and CoO, respectively. The SO₂ is induced into an absober (cap-typetower), and then absorbed in water solution of sodium hydoxide to beconverted into solution of sodium sulfite (Na₂SO3). The solution ofsodium sulfite is dained out from the absorber.

In recovery of nickel and cobalt, the oxides of nickel and cobalt aremilled, and then nickel and cobalt are extracted from the miled oxidesof the metals in ammonia solution. As the extracted nickel and cobaltcontains water soaked therein during the previous extraction process, anadditional process of drying the soaked nickel and cobalt is required.This makes the whole processes for recovery of metals complex. Further,ammonium salts of nickel and cobalt are formed in the extraction processand thus make separation of the metals incomplete. Because of theabove-mentioned disadvantages, a process for roasting proceeds withoutrecovering nickel and cobalt.

The conventional process comprises inducing the oxidized waste catalystswith sodium carbonate (Na₂CO₃) continuously and quantitatively into arotary kiln, and maintaining the rotary kiln at a temperature of 600° C.to melt the oxides of the metals with the sodium carbonate therein. Inthis process, aluminium may be obtained in a form of mixture such aswater-insoluble sodium aluminate. Vanadium and molybdenum are obtainedin the form of their sodium salts, such as water-soluble sodium vanadate(NaVO₃) and sodium molybdate (Na₂MoO₄).

The conventional process further comprises milling the roasted productobtained in the preceeding process, agitating the milled roasted-productin the warm water at a temperature of 80° C. and then leaching theformed sodium salts for one hours, washing the leachates at one ortwice, controlling the washing liquid at pH 8.0, and agitating thewashing liquids with ammonium chloride (NH₄cl) mixed therein toprecipitate crystals of amonium metavanadate (NH₄VO₃).

In this process, the volume of ammonium chloride is used more thanthioretical volume. Further, after separaing the precipiates from themother solution, pH of the mother solution is lowered at the range of pH2˜3. And then, solution of ammonium chloride is added to the mothersolution lowered at pH 2-3 so as to remove sufate ion (SO₄ ⁻²) therein,and thus calcium sulfate (CaSO₄₎ is precipitated. After removing theprecipitates of calcium sulfate and then increasing pH of the mothersolution, solution of calcium chloride is added to the mother solutionso as to precipiate calcium molybdate (CaMoO₄). molybdenum oxides can beobtained by leaching and washing the precipiated calcium molybdate, andthen decompounding the precipiated calcium molybdate with hydrochloricacid.

DISCLOSURE OF INVENTION Technical Problem

The conventional method has disadvantages as followings. The methodrequires expensive equipments, such as a rotary Kiln, for roasting at ahigh temperature (900° C.). Because costs is very high, a recovery ofnickel wolud not be performed. Though the waste catalysts containaluminum oxide therein at a rate of 65 percentage, the aluminum oxide isdiscarded in a form of water-insoluble aluminum compound, therebyresulting in waste of resources.

Technical Solution

It is an object of the present invention to provide methods ofrecovering valuable matals from the waste catalysts used in the VRDS,which can increase high yield of vanadium and molybdenum from the wastecatalyst at lower temperature and further recover aluminum as well asnickel and coblat without additional processes.

It is further object of the present invention to provide methods ofrecovering valuable matals from the waste catalysts without dischargingwaste water containing ammonia nitrogen, thereby reducing costs forpurifying waster water.

In order to solve the above disadvantages, the present inventioncomprises pre-treating the waste catalysts for deoiling anddesulfurization; forming sodium aluminate, sodium vanadate and sodiummolybdate as water-soluble reactants, and nickel oxide, cobalt oxide aswater-insoluble reactants by reacting the pre-treated waste crystals insolution of sodium hydroxide at a temperature of 135˜160° C.; andleaching the water-inslouble nickel oxide, cobalt oxide and impurities,thereby remaining the water-soluble sodium aluminate, sodium vanadateand sodium molybdate in the solution.

The present invention further comprises heating the filtrate containingthe sodium aluminate, sodium vanadate and sodium molybdate so as toincrease a temperature of the filtrate over a temerature of 80° C., andagitating the filtrate with adding hydrochloric acid or sulfhuric acidtherein so as to maintain pH 9.5; forming aluminum oxide at thetemperture over 110° C. with heat of the reaction; and recovering thealuminum oxide by leaching.

Furthermore, the present invention comprises forming a solutioncontaining sodium vanadate and sodium molybdate bt treating the wastecatalysts; heating the solution with the solution maintained in pH1.0˜−1.0; and precipitating molybdenum oxide and vanadium oxide in thesolution by aeration thereof.

The present invention further comprises adding ammonia water to thesolution in which molybdenum oxide and vanadium oxide are precipitatedand thus agitating the mixtured solution so as to precipitate amoniummetavanadate with ammonium molybdate remaining in the solution; andrecovering and separating the crystals of the precipitated amoniummetavanadate from the solution.

Advantageous Effects

The present invention can increase yield of vanadium and molybdenum fromthe waste catalyst at lower temperature and further recover aluminum aswell as nickel and coblat without additional processes.

Further, the present invention can recover valuable matals from thewaste catalysts without discharging waste water containing ammonianitrogen, thereby reducing costs for purifying waster water.

in addition, the present invention can reduce costs of maunfacturingbeecause it does not require expensive equipments, such as a rotaryKiln, for roasting at a high temperature (900° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow diagram of the process according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is desribed in detail with reference to theattached drawing.

The waste catalysts used in the ‘Vacuum Residue Desulfurization’ (VRDS)process for desulfurization of pertoleum may be pre-treated by the knownvarious methods. That is, the pre-treatments of the waste catalysts,such as oil-removing, sulphur-removing, and oxidization of metals, areaccomplished by generally known processes. For example, oils soaked inthe waste catalysts are removed by heating the catalysts at atemperature over the boiling point of oil.

The deoiled waste catalysts are maintaining at a temperature of 400° C.with heating in the deoiling process. Before cooling, the wastecatalysts are induced into the roasting furnace and roasted with thesupplied oxygen at a temperature of 400˜600° C.

In the roasting process, the metals, such as molybdenum, vanadium,nickel, cobalt, in the waste catalysts are oxidized and thus covertedinto their oxides, such as MoO₃, V₂O₃, NiO, CoO, and also the sulphur isoxidized and converted into sulphuric acid gas (SO₂).

The sulphuric acid gas is absorbed in solution of sodium hydroxide(NaOH) and converted into sodium sulfite (Na₂SO₃), which is drained out.

The waste catalysts are dissolved in solution of sodium hydroxide andthen the solution is agitated. the non-reactants including NiO, Fe2O3are leached and thus separated from the solution.

Preferably, 80 PBW (Parts By Weight) of and 80 PBW of sodium hydroxideare poured and then mixed in a reactor equipped with an agitator. Inthis process, the sodium hydroxide is dissolved with heat ofdissolution. The solution is heated pressurelessly until the temperatureof the solution reached at 135˜160° C. by adding 100 80 PBW of theoxidized waste catalysts therein.

To react the waste catalysts in the solution at 160° C. for 2˜3 hours,NiO, FeO and CoO would not be dissolved and thus remain in the solution.400 PBW of water is added so as to prevent reprecipitation of reactantsby dilution of the solution. Then, the residues including NiO areleached from the solution. Nickel can be simply recovered from theresidues.

Then, aluminum is recovered from the filtrate. The filtrate containssodium aluminate (NaAl(OH)₄). To separate the sodium aluminate from thefiltrate, the filtrate is stirred with an agitator and heated at atemperature of 85˜90° C. and then sulphuric acid or hydrochloric acid(20˜30%) is added into the filtrate. The addition of the acid to thesolution should be controlled to be maintained at pH 9.5. In thisprocess, aluminum oxide (Al₂O₃) is poducted and thus leached from thesolution. The aluminum oxide is washed with water until vanadium is notdetected in the water. The water in the aluminum oxide is dried withsuction of a vacuum pump.

The above processes for recovering aluminum may be applied to therecovery of vanadium in the same manner. In the process of recoveringvanadium, aluminum oxide is replaced with sodium aluminate and sodiumtungstate exist in a form of water solution.

In the reaction of filtrate with HCl solution, the reaction temperatureand the basicity or acidity are very critical.

The beolw reaction formulars show various products of aluminum oxideaccording to gradients of temperature at pH 9.5˜14.

NaAl(OH)₄+HCl=Al(OH)₃+NaCl+H2O (0° C.˜normal temperature)  {circlearound (1)}

NaAl(OH)₄+HCl=AlO(OH)+NaCl+2H2O (80° C.˜95° C.)  {circle around (2)}

2NaAl(OH)₄+2HCl=Al₂O₃+2NaCl+5H2O (100° C.˜120° C.)  {circle around (3)}

In the reaction {circle around (1)}, the reactant, Al(OH)₃ can not beseparted by leaching. Accordingly, a rotary kiln should be required forrecovery of aluminum in the condition of the reaction {circle around(1)}.

In the reaction {circle around (3)}, the reactant, AlO(OH) by thereaction {circle around (2)} may remain but may also be leached.Therefore, the condition of reaction temperatures in the reaction{circle around (3)} is accepatable. When the reaction proceeds at atemperature over 80° C., the temperature get increased over 110° C. bythe heat of reaction.

Accordingly, the above process of recovering aluminum is required to beproceeded at a temperature over 110° C. because the reactant, Al(OH)₃ isnot produced at the temperature. The temperature of the reaction is notliminted by the upper limit but preferably maintained at a temperatureof 100° C.

As the filtrate is maintained at 120° C. by applying pressure, solutionof HCl is added to the filtrate of pH 9˜14. Then, sole Al₂O₃ may beobtained by removing sodium oxide (Na₂O) from the filtrate. There remainsodium vanadate (NaVO₃) and sodium molybdate (Na₂MoO₄) in the filtratefrom which Al2O3 is removed. Preferably, the filtrate is agitated belowpH 1 (pH −1.0) at 85° C. until the reaction is completed.

As shown in the following reaction formulas I and II, the filtrate isagitated below pH 1 at 85˜100° C. and further aetated thereincontinuously or periodically. As a result of the process, mixtures ofmolybdenum oxide and vanadium oxide are precipitated in the solution.The precipitated molybdenum oxide and vanadium oxide may be obtained byleaching.

While the filtration is aerated by blowing air, reaction of hydrationoccurs and thus the metal oxides are precipitated in the solution ofreaction. The aeration allows hydration to accur at a lower temperature,thereby allowing additonal heating to be eliminated. In this reaction,molybdenum oxide and vanadium oxide are precipitated as amorphouscrystal and thus may be obtained by leaching and washing.

In the above process, acid solution should be used to maintain thesolution below pH 2, preferably below pH 1 at a temperature of 80° C.This temperature of reaction is dominantly lower than that of theconventional procsess, which makes heating equipments of high price tobe useless.

The present invention may further comprise adding ammonia water to thesolution in which molybdenum oxide (MoO₃) and vanadium oxide (V₂O₅) areprecipitated, agitating the mixtured solution and thus precipitatingamonium metavanadate (NH₄VO₃) and ammonium molybdate ((NH₄)2MoO4) byusing diiference of solubilty thereof; and recovering and separating thecrystals of the precipitated amonium metavanadate and ammonium molybdatefrom the solution.

After sepating ammonium molybdate from the mother solution, molybdenumoxide (MoO) and vanadium oxide (V₂O₅) are furhter added to the mothersolution with amonium water. Thus, molybdenum oxide (MoO₃) and vanadiumoxide (V₂O₅) are dissolved in the mother solution by re-heating, andthen amonium metavanadate is obtained by cooling the mother solution.These processes are repeated until the specific weight of the mothersolution reaches to 2.5.

Through the processes, ammonium molybdate and amonium metavanadate ofhigh purity are obtained by minimizing dissoved amonium metavanadate.

After the process, the specific weight of mother solution may vary asquantity of water or molybdenum in the waste catalyst. When the specificweight is below 2.5, the mother solution may be reused as reactionsolution. When the specific weight is over 2.5, the mother solutionbecomes ammonium molybdate with 0.0% vanadium by cooling and thenremoving amonium metavanadate therefrom.

Molybdenum oxide and/or vanadium oxide may be obtained by pyrolizing atleast one of the amonium metavanadate and ammonium molybdate. Amonia gasgenerated in the process is converted into amonia water and then reusedas a form of amonia water in the process.

INDUSTRIAL APPLICABILITY

The present invention can increase yield of vanadium and molybdenum fromthe waste catalyst at lower temperature and further recover aluminum aswell as nickel and coblat without additional processes.

Further, the present invention can reduce costs of manunfacturingbeecause it does not require expensive equipments, such as a rotaryKiln, for roasting at a high temperature (900° C.).

Additionally, the present invention can recover valuable matals from thewaste catalysts without discharging waste water containing ammonianitrogen, thereby reducing costs for purifying waster water.

1. A method of recovering valuable matals from the waste catalysts inVRDS, comprising: pre-treating the waste catalysts for deoiling anddesulfurization; forming sodium aluminate, sodium vanadate and sodiummolybdate as water-soluble reactants, and nickel oxide, cobalt oxide aswater-insoluble reactants by reacting the pre-treated waste crystals insolution of sodium hydroxide at a temperature of 135˜160° C.; andleaching the water-inslouble nickel oxide, cobalt oxide and impurities,thereby remaining the water-soluble sodium aluminate, sodium vanadateand sodium molybdate in the solution.
 2. A method according to claim 1,further comprising heating the filtrate containing the sodium aluminate,sodium vanadate and sodium molybdate so as to increase a temperature ofthe filtrate over a temerature of 80° C., and agitating the filtratewith adding hydrochloric acid or sulfhuric acid therein so as tomaintain pH 9.5; forming aluminum oxide at the temperture over 110° C.with heat of the reaction; and recovering the aluminum oxide byleaching.
 3. A method of recovering valuable matals from the wastecatalysts in VRDS, comprising: forming a solution containing sodiumvanadate and sodium molybdate bt treating the waste catalysts; heatingthe solution with the solution maintained in pH 1.0˜−1.0; andprecipitating molybdenum oxide and vanadium oxide in the solution byaeration thereof.
 4. A method according to claim 3 further comprisingadding ammonia water to the solution in which molybdenum oxide andvanadium oxide are precipitated and thus agitating the mixtured solutionso as to precipitate amonium metavanadate with ammonium molybdateremaining in the solution; and recovering and separating the crystals ofthe precipitated amonium metavanadate from the solution.